The invention relates to a pneumatic, reciprocating rotary driving mechanism unit for operating a shut-off member in a shut-off valve, comprising a substantially closed housing, in which a drive shaft is journalled which can be connected to said shut-off member, a pneumatic control valve for controlling said drive shaft and first signal transmitting means for delivering control signals to said pneumatic control valve. The driving mechanism as disclosed in Dutch laid-open publication no. 7512312, which is used with peripheral equipment in practice, fits the above description. Such driving mechanisms are generally used for operating butterfly valves, plug valves and ball valves as well as also lamellas in dampers, wherein the angle of rotation of the drive shaft is limited to maximally 180° and usually to 90°. To this end, all kinds of pneumatic components and control equipment are mounted on the outside of the housing, such as the control valve and a signal transmitter.
In a functional situation wherein the drive shaft only needs to be capable of taking up two positions corresponding with an open position and a closed position of the shut-off valve, such peripherals generally comprise a so-called solenoid which is mounted on the outside of the housing, which solenoid converts the electrical control signals from a central electronic control system into pneumatic control signals for operating a pneumatic control valve, which also forms part of the solenoid. A switch box is mounted on to the housing via a bridge, in line with the free end of the drive shaft, which switchbox transmits information about, amongst other things, the actual rotational position of the drive shaft to the central control system, such as a PLC unit. The switch box and the solenoid are interconnected by means of a line outside of the housing for the purpose of exchanging information.
In the functional situation wherein the drive shaft is to be driven in a modulating manner, that is, enabling continuously variable adjustment of the valve between an open position and a closed position, a so-called positioner is mounted on the outside of the housing instead of said solenoid and said switch box, which positioner is capable of continuously variable adjustment of the shut-off member of the shut-off valve between 0-100%, for example by means of a control current of 4-20 mA. Lines are provided outside of the housing for operating the shut-off member.
Units such as a solenoid, a switch box or a positioner must be capable of communication with all kinds of control equipment. This implies that a great many variants of each of the aforesaid components are required. As a result of this it has appeared to be very difficult, costly and time-consuming in practice to change the functionality of a pneumatic driving mechanism. In addition, the driving mechanisms according to the prior art are quite vulnerable, due to the way in which the peripherals are connected to the housing and to each other.
The object of the invention is to provide a solution for the above drawbacks and to meet the aforesaid need. In order to accomplish that objective, the driving mechanism according to the invention is characterized in that the housing consists of a base part, in which the drive shaft and the pneumatic control valve are present, and a first function part, in which the first signal transmitting means are present, which first function part is detachably and exchangeably connected to said base part so as to make it possible to exchange said first function part for a second function part containing second signal transmitting means of a type different from the first signal transmitting means, which first function part is exchanged for the second function part for the purpose of changing the manner in which the drive shaft can be controlled. The invention is based on the insight that some of the components of which the driving mechanism is built up are required for every function that is desired, whilst other components are only required for specific functions. According to the invention, the former components are housed in the base part. By housing the latter components in a specific function part, which is detachably connected to the base part, a simple exchangeability of the function part and thus of the functionality of the pneumatic driving mechanism is effected without any adaptations or the exchange of the base part being required. It is not so much the pneumatic components that make up the difference between the function parts mutually, but rather the electronic components that are present therein, since it is the latter that determine the functionality in question and that can be considered as signal transmitting means. The function part can on the one hand be designed as a black box without control buttons or information panels, but on the other hand it may be designed to comprise sensors, switches, various electrical terminals, manual operation provisions, for example for emergency operation, LED's, LCD's, etc. The integration thereof in the function part obviates the need for additional electrical wiring and/or pneumatic connections.
As an aside it is noted that German utility model DE 298 18075 U1 discloses a fluidic linear actuator comprising a housing in which a piston whose piston rod extends outside the housing is present. Present on the housing is a two-part control housing. A fluidic feed connection is formed in the first part, whilst an electronic control unit is present in the second part, whereby there is an electrical connection between the first part and the second part so as to enable electronic data transfer between the first part and the second part. Present in the first part is a signal transmitting valve, which delivers pneumatic control signals to a pneumatic control valve which is also present in the first part. The actuator disclosed in said publication is only suitable for actuating the piston in one and the same manner, whereby the second part, on the other hand, can be adapted to enable communication with various types of artificial intelligence remote from the actuator.
Advantageously, at least one mechanical portion of a position indicator, which is movable in dependence on the rotation of the drive shaft, is housed in the base part for the purpose of showing and/or transmitting information about the rotational position of the drive shaft. Integration of the position indicator in the base part on the one hand makes it possible to realise a compact and robust construction, whilst on the other hand no vulnerable external lines for the control system are required. By housing the mechanical components of the position indicator at least in part in the base part and housing the electronics in the function part it becomes possible to prevent a situation wherein mechanisms operate between the base part and the function part in a vulnerable manner. In addition, no mechanical adjustment of the position indicator is required when a function part is being connected to a base part. The function part converts the movement or the position of the mechanical part of the position indicator into electronic information for feedback to a control system.